There are various applications in which is it desirable to deposit a coating onto at least a portion of a sheet of material. For example, in some embodiments, the electrodes of batteries are produced by applying a layer or coating to a sheet, and then cutting the sheet into portions of a suitable dimension. Of particular importance is that the layer be applied at a uniform thickness. In some embodiments, the layer or coating is not applied to the sheet in the region where the sheet will subsequently be cut.
Based on this, it is necessary to provide a system that can apply a uniform layer or coating to a sheet, with the ability to enable and disable the application of that layer as required. FIG. 1 shows a system which may be used to apply such a layer of coating to a sheet.
The system 100 includes a sheet of material 10 to be coated, which typically proceeds through the system by passing over one of more rollers 15.
The coating is typically held in a tank or reservoir 30. The coating is drawn from the reservoir 30, through conduit 31 by pump 40. The coating is then passed through conduit 32 by the action of the pump 40.
In the case where coating is not being applied to the sheet 10, bypass valve 50 is open while supply valve 60 is closed. This allows the coating that is pumped through conduit 32 to pass through conduit 33 and back to reservoir 30.
In the case where coating is being applied to the sheet 10, the bypass valve 50 is closed, while supply valve 60 is opened. This permits the flow of coating through conduit 62 to the nozzle 70, and onto the sheet 10. While the supply valve 60 is open, the coating is discharged by the nozzle 70. However, when the supply valve 60 is closed, the pressure needed to propel the coating through the nozzle 70 is eliminated. In some cases, this causes excess coating material to remain in the cavity, or manifold 71, and the lips 72 of the nozzle.
When the supply valve is next opened, this excess material may cause an uneven application of coating to the sheet 10. FIG. 2 shows an example of the result of this phenomenon on the coated patch thickness. Coated patch 500 is shown as a cross-section profile of thickness “x” applied to web 10. As the sheet moves toward the left, starting profile 520 is thicker than the rest of the coating 500. This excess material 510 is due to the residual coating material that remained in the nozzle 70 after the supply valve was closed 60. In this figure, the ending profile 525 is shown to be uneven, as the valves may be transitioning while the coating is still being applied. Such an uneven coating may be unacceptable.
Therefore, to prevent this uneven application, a fluid suction mechanism 80′ may be used, as shown in FIG. 1. This fluid suction mechanism is used to draw the excess coating that is left in the manifold 71 or on the lips 72 away from the nozzle 70.
In operation, pump 40 draws coating material from reservoir 30. The coating material passes through conduits 31, 32 and is directed toward the nozzle 70, where it is discharged onto the sheet 10 as the sheet is drawn past roller 15. To stop the flow of coating onto the sheet 10, the bypass valve 50 is opened and the supply valve 60 is closed, thereby diverting the coating material through conduit 33 and back into the reservoir 30. To remove excessive coating material that may be present in the manifold 71 or on the lips 72 of the nozzle 70, valve 85 is opened to suction source 80 so that fluid is drawn by vacuum through conduit 86 which is in fluid communication with die manifold 71. The suction source 80 is typically comprised of a vacuum reservoir tank in communication with a suction pump to create a draw of fluid from die cavity 71 when valve 85 is opened. Coating fluid material is collected in said reservoir tank and periodically removed for reuse or, more often, discarded as waste material.
To restart the flow of coating onto the sheet 10, valve 85 is closed to remove the vacuum drawing fluid through conduit 86. Bypass valve 50 is closed while supply valve 60 is opened.
In some embodiments, the nozzle 70 can be moved relative to the roller 15 so as to minimize the amount of coating material that may drip out onto the sheet 10. The nozzle 70 may move in the direction of the sheet (i.e. up and down in FIG. 1). In other embodiments, the nozzle 70 moves orthogonal to the sheet (i.e. in and out of the page). The movement of the nozzle 70 may be linear or rotational.
It would be advantageous if there were no need for a fluid suction mechanism in the system and the associated handling and disposal of coating fluid. Furthermore, it would be beneficial if there were an enhanced system and method for creating a coating on a sheet, where the starting profile and ending profile may be controlled to create various patterns at high production rates without the use of a suction mechanism.